With A Thousand Lies
by MarzBarz
Summary: Castiel raises Dean Winchester from Perdition, but Dean Winchester is not his true charge; Sam Winchester is. Season 4 AU, gets gradually darker as it goes.


**A/N:** So this was written as a pinch-hit for the Blind Sassy Exchange over on Tumblr. I pounded this sucker out in around 24 hours after someone else dropped out. I'm actually really really proud of this, and I hope you enjoy it! Warning, it gets kind of dark towards the end, or dark for me anyways.

* * *

Once Castiel raises the Righteous Man from Perdition, he expects to never see Dean Winchester again. He is surprised when Zachariah tells him this is not the case. He is being assigned to Sam Winchester, the boy with the demon blood, to train his powers so that he will be powerful enough to kill Lilith. Zachariah explains that while Sam is being trained by the demon Ruby, his powers are not growing quickly enough, so Castiel is being sent to speed up the process.

Castiel knows better than to question his orders, but he is confused; the demon blood running through Sam Winchester's veins makes him an abomination. He does not speak up, but privately he wonders about this assignment. With the seals breaking, he supposes that they have no choice but to use whatever weapons they have available, including the boy with the demon blood.

* * *

Castiel expects to be meeting Sam Winchester when he first uses his earthly vessel. Instead he feels the pull of a summoning ritual, and his introduction to the Winchester is brothers is through Dean. Castiel is not impressed by their meeting; Dean stabs him with a demonic blade, shows him no respect, has no faith, and is angry with him for something he could not control. He tried to warn the psychic and it is not his fault that she refused to listen. He hopes that his first meeting with Sam Winchester has more positive results.

He first talks to Sam Winchester in Robert Singer's kitchen, immediately following the breaking of the second seal. He is largely unsurprised when the first thing Sam does upon awakening to a stranger in the house is draw a knife from beneath his pillow and throw it with perfect accuracy and startling speed; that does not mean he is not frustrated when the knife buries itself in his vessel's heart. "Enough," he snaps, pulling the knife out of his chest. "I am no threat to you or your brother, Sam Winchester."

"Because things that appear in the middle of the night and don't wake anyone else up aren't unnatural," Sam says, pulling a gun from somewhere and aiming it at Castiel's face.

"I am an angel of the lord," Castiel says.

"Wait, you're Castiel?" Sam says, frown smoothing out into a slightly awed expression. "You're the one who saved my brother from Hell?" When Castiel nods, Sam smiles widely. "Thank you so much. It's an honor to meet you," he says, moving to Castiel and holding out his hand. "I've heard about you."

Castiel stares at the extended hand for a moment before taking it in one of his own. "And I you. Sam Winchester, the boy with the demon blood." He feels a pang of some emotion when Sam's face falls, but continues speaking; they have much to discuss. "I know about what you and the demon Ruby have been doing."

"I can stop if that's what you want," Sam says hurriedly. He isn't looking at Castiel, but he hasn't removed his hand from Castiel's either. "I just, it was a reason to keep going, and I was just using it as a way to kill Lilith –"

"I'm here to help you learn to use your powers," Castiel says, cutting Sam off. "We need you to be strong enough to kill Lilith. You have made a good start in your work with the demon Ruby, but you need to be far stronger than this to kill Lilith. She is a far higher class of demon." Sam's head snaps back up, eyes wide with surprise when they meet Castiel's. "I will be attending your future training sessions with the demon to speed your instruction along."

"Alright. Should I…I mean, I suppose I should tell Dean about me and Ruby soon, huh," Sam says, though he seems to be talking more to himself than to Castiel. Castiel takes this as a sign that the conversation is over and flies away.

* * *

Castiel soon finds out that the best laid plans of Winchester men will always go awry. Sam doesn't tell his brother about his powers; apparently Uriel sent Dean on a trip to the past that was necessary to resolve a timeline paradox before he had the chance. So naturally Uriel tells Dean to stop Sam from using his powers or Uriel will stop him, and then leaves Dean in the warehouse where Sam is practicing with both Ruby and Castiel.

Castiel is confused when he senses Uriel and Dean both in the warehouse, but he doesn't have long to wonder about it; Dean bursts in just as Sam is about to finish his fastest exorcism yet and goes straight for Ruby with the demonic knife. Sam immediately moves to intervene, and the whole situation quickly spirals out of control.

Castiel steps in when it becomes obvious Dean will stop at nothing to kill Ruby; though she is a demon, using her as a source of demon blood is easier than capturing a demon whenever Sam needs more. "Stop, Dean. We need her."

"What the fuck are you even doing here, Cas?" Dean snaps, turning towards him with a furious expression. "Your dickbag pal, Uriel, told me that Sam had to stop using his powers or he would kill him. What the fuck are you doing standing around doing nothing while this bitch makes him use them?"

"I am under orders to help your brother train his powers to kill Lilith," Castiel says, filing the information about Uriel away for later. He does not know why Uriel said this. "I can only assume that Zachariah has not told the other angels about my assignment."

Dean glares at Castiel, and Sam finally breaks his silence. "Dean, my powers are helping. If I pull the demon, the host has a better chance of survival. It doesn't kill them like the knife does, or the Colt did."

The argument grows from there, and Castiel figures it is not his place to intervene here. He leaves, and makes sure to take the demon with him.

* * *

"Uriel. Why did you threaten Sam Winchester's safety over something that you know I was ordered to have him do?"

"You know why, Castiel. For everything to go according to plan there needs to be bridges burned between the brothers. I am under orders to do my best to make that happen. You know what Sam Winchester must do; for that to come to pass, Dean must not be standing beside him. We need their bond to be broken."

Castiel nodded, but something inside of him wanted to argue with Uriel's actions; it seemed wrong to pit the brothers against each other. But it was not his place to argue, and he flew away with a rock in the pit of his stomach that his vessel recognized as guilt.

* * *

Castiel was vaguely worried that Sam would want to stop training after Dean found out, but the young man was there with the demon at the appointed time to train. Castiel didn't ask questions about the bruise on Sam's cheek, and Sam didn't mention his brother; they simply got to work.

Castiel found himself developing a routine. Once a week he would train with Sam and Ruby, developing Sam's powers. Every other week the dosage of demon blood would be increased. When he was not training with Sam he would defend a seal with his brethren; the breaking of the seals needed to be delayed as long as possible to ensure Sam would be ready when it was time to break the final seal.

Everything seemed to be moving along quickly and going according to plan until Anna Milton appeared on the radar of Heaven, Hell, and the Winchesters. Castiel was informed of her existence the day after a training session with Sam, and ordered to take her captive. He was paired with Uriel, and they went to Anna only to find the Winchesters there as well.

When they were banished, Castiel took the opportunity to think on what Ruby told him; Sam had not only failed to kill Alastair, his powers had almost no effect. This was troubling; though he was the same class of demon as Lilith, he was still significantly weaker, and Castiel hadn't thought Sam's powers would be so ineffective at this point in their training. He decided to up Sam's training as soon as the matter with Anna was over.

* * *

The matter resolves in a manner that Castiel has come to anticipate whenever the Winchesters are involved; messily and not according to plan. Anna retrieves her Grace and flees, Alastair's host body is destroyed but the demon itself escapes capture, and the Winchesters trust in angels reaches a new low.

Castiel realizes quickly that he is going to have to work hard to fix the damage that has been done to his relationship with both Winchesters, especially Sam. He had not realized how much he enjoyed Sam's presence and conversation during their training sessions until the conversation never comes during their first post-Anna training session. Instead, Sam simply follows Castiel's instructions; he doesn't even protest when Castiel increases the dose ahead of schedule. Ruby puts up more of an argument when Castiel informs them that training is going to be every other day from now on, and that the dosage will be increased every week. Castiel wants the friendliness that Sam once had to return, but he isn't sure how to do it and simply continues to train him instead.

Sam's strength increases rapidly under this new training regimen, and soon Sam is back to the way he was around Castiel before Anna came into the picture. Then Castiel starts to notice that Sam is a little…off. He remembers the Sam he first met, who was so humbled by the existence of angels and wanted nothing more than to do the right thing, and realizes that the Sam standing before him with a cruel smirk is not the same man he met back then. This becomes all the more obvious when Sam's eyes slide to a demonic black just before the demon tied to the chair is pulled from its host.

"Sam?" Castiel says, staring at the human's pitch-black eyes.

Sam lets his breath out through his nose, then grins viciously. "I can do it, Castiel," he says. "I think I could kill a low-level slug like this if I tried." He smiles, and there is something dark at the edges of that smile that make Castiel want to reach for his sword. He glances at Ruby, standing behind Sam, and sees a mix of reverence, adoration and pride that worries him. When he looks back at Sam, the dark expression is gone and Sam looks like any other human again.

* * *

Castiel learns just how far from human Sam really is when Alastair begins kidnapping Reapers to break a Seal. The Winchesters investigate and rescue the reapers, saving the Seal, and Alastair is captured when he goes after Dean for revenge. Sam's powers save his own life, though he isn't fast enough to save the life of the psychic Castiel accidentally blinded.

Castiel hopes this is the end of the Winchesters involvement, but he has realized that with the Winchesters the worst case scenario is also the scenario most likely to happen. This proves true when Zachariah orders Castiel and Uriel to make Dean Winchester torture Alastair for information. Castiel realizes quickly that the only way Sam will let his brother do this is if he doesn't know it's happening, and explains the situation to Dean while Sam is asleep. Dean is resistant to the angels' orders at first, but he gives in quickly and the torture begins.

Hours later Alastair has yet to break, and Castiel has stopped focusing on what is happening within the devils trap the demon is being help in. He knows the longer it takes Dean to break Alastair, the more likely it is that Sam will find them, and when Sam comes he will be far angrier than he has ever been since his brother was returned.

When Castiel turns around to check on Dean's progress he finds Alastair free of his bindings and in the process of killing Dean. Castiel flits into the room and grabs the demonic blade from where Dean dropping it, aiming to drive it into Alastair's heart. The demon turns and the blade is imbedded in its shoulder instead, and a brief struggle ensues.

Castiel manages to hold his own for a moment, but he is overpowered when Alastair shoves his vessel's spine onto a piece of protruding metal and drags him down, keeping the metal at a point where his vessels limbs all become inoperable and he can't heal the damage to move them. He thinks that all hope is lost when Alastair begins reciting an invocation to send him back to Heaven.

Castiel can feel his Grace being dragged out of his vessel when Alastair is suddenly ripped away from him and pinned against the wall. Castiel is surprised but grateful when Sam walks in, and uses the time Sam spends torturing Alastair with his powers to fully heal the spinal damage done to his vessel and removes himself from the post. He pays close attention to what Alastair says, and comes to a horrifying realization; he knows who is killing the angels, and it is a traitor in their midst.

While Castiel is figuring this out, Sam has decided that Alastair is telling the truth. Castiel can't help the shiver that runs up his spine at Sam's feral grin as the hunter extends his hand and snarls "Now I can kill." Castiel is no longer taken by surprise when Sam's eyes flood black while he uses his powers, but when the light hits them a certain way Castiel thinks he can see flecks of yellow where the pupils would be. Sam isn't even breathing hard when he kills Alastair, and as he turns to his brother Castiel is sure he sees the hunter's pupils turn yellow in the wake of the black. Castiel wants to address the matter, but Sam is already focused on his brother and Castiel has other business to attend to; he needs to deal with Uriel.

* * *

The day the 65th seal breaks, Castiel prays that no one will inform the Winchester brothers. When told, the brothers and Sam especially will want to go after Lilith immediately to stop her breaking the final seal. Castiel is well aware of what the 66th seal is, and what he has been training Sam to do; he has simply come to realize that he does not want Sam to do it. When he looks at Sam now, there is always a shadow of yellow in his eyes. Sam himself has changed much since he began training with Castiel; where he once shrank into himself to put people at ease, he now walks with all the confidence of a king. He is no longer humbled by Castiel's angelic powers, nor is he reverent of angels as he was when Castiel first met him. Though he may sometimes hold a conversation with Castiel, it doesn't take long before the talk turns to killing Lilith, or to finding ways to further increase his power. Castiel finds that he misses the old Sam.

Castiel has made up his mind to tell Dean the truth about the seals when Zachariah sends Rachel to bring him to the Green Room. It doesn't take him long to realize that his superiors are aware of what he wanted to do, and that they were trying to keep Castiel there to prevent his escape. Each time Castiel attempts to fly away, an angel appears and keeps him occupied. Finally he resorts to smashing apart one of the glass objects in the room and using it to cut his arm open, the regret and guilt that has built up during his imprisonment forced down by his determination.

Castiel finishes a banishing sigil just as Zachariah appears in the room, demanding to know what he's doing. He banishes his superior and flies for St. Mary's Convent, where Azazel first slaughtered the nuns and spoke to Lucifer. He is forced to land outside the convent, and runs in only to have Ruby close the door to the altar in his face. He immediately attacks the door with his angelic blade, hacking through it piece by piece and yelling warnings to Sam, but he is too late; he gets through the door in time to see Lilith slump down, bleeding, as Sam throws his head back in victorious laughter that makes Castiel instinctively raise his sword.

Sam's eyes are yellow.

Lilith's blood begins to run in a circle towards the center of the room, and Sam's laughter tapers off as he notices the changes. Castiel can do nothing but stare as the blood form a door to the Cage, though he can dimly hear Ruby crowing something in the background as both Sam and Dean yell at her. He snaps to attention in time to see Sam, eyes still yellow, throw a hand out with a snarl and physically rip Ruby from her host, then tear her demonic form apart with his bare hands.

Castiel moves slowly closer to Dean as a beam of light emits from the circle of Lilith's blood. Sam is staring at the light with wide eyes, his expression a cross between horror and wonder, leaning forwards as if he's drawn to it, and Castiel closes his eyes. He pictures the Sam he met almost a year ago, and thinks that this is a betrayal of that boy who said it was an honor to meet an angel. Dean looks as if he wants to run forwards and drag his brother back, so Castiel grabs his arm and says "We have to go. There is nothing we can do." He flies them away from the convent before Dean can protest, thinking _but there was something I should have done. I'm so sorry, Sam._

* * *

__Prompt 1: Dean may be the one that Castiel raised from Hell, but his true charge is Sam. Cue: training sessions and demon blood rationing to turn Sam into a creature vicious enough to kill Lilith. S4AU


End file.
